Vibrating flowmeters or conduit sensors, such as Coriolis mass flowmeters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that contains a flowing material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness, and damping characteristics of the conduit and the material contained therein.
It is well known to use vibrating meters to measure mass flow and other properties of materials flowing through a pipeline. For example, vibrating Coriolis flowmeters are disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and also. Re. 31,450 to J. E. Smith of Nov. 29, 1983. These vibrating meters have one or more fluid tubes. Each fluid tube configuration in a Coriolis mass flow meter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, lateral, or coupled type. Each fluid tube is driven to oscillate at resonance in one of these natural modes. The vibration modes are generally affected by the combined mass, stiffness, and damping characteristics of the containing fluid tube and the material contained therein, thus mass, stiffness, and damping are typically determined during an initial calibration of the vibrating meter using well-known techniques.
Material flows into the flow meter from a connected pipeline on the inlet side of the vibrating meter. The material is then directed through the fluid tube or fluid tubes and exits the flow meter to a pipeline connected on the outlet side.
A driver, such as a voice-coil style driver, applies a force to the one or more fluid tubes. The force causes the one or more fluid tubes to oscillate. When there is no material flowing through the flow meter, all points along a fluid tube oscillate with an identical phase. As a material begins to flow through the fluid tubes, Coriolis accelerations cause each point along the fluid tubes to have a different phase with respect to other points along the fluid tubes. The phase on the inlet side of the fluid tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed at two different points on the fluid tube to produce sinusoidal signals representative of the motion of the fluid tube at the two points. A phase difference of the two signals received from the sensors is calculated in units of time.
The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the fluid tube or fluid tubes. The mass flow rate of the material is determined by multiplying the phase difference by a flow calibration factor. The flow calibration factor is dependent upon material properties and cross sectional properties of the fluid tube. One of the major characteristics of the fluid tube that affects the flow calibration factor is the fluid tube's stiffness. Prior to installation of the flow meter into a pipeline, the flow calibration factor is determined by a calibration process. In the calibration process, a fluid is passed through the fluid tube at a given flow rate and the proportion between the phase difference and the flow rate is calculated. The fluid tube's stiffness and damping characteristics are also determined during the calibration process as is generally known in the art.
One advantage of a Coriolis flow meter is that the accuracy of the measured mass flow rate is not affected by wear of moving components in the flow meter, as there are no moving components in the vibrating fluid tube. The flow rate is determined by multiplying the phase difference between two points on the fluid tube and the flow calibration factor. The only input is the sinusoidal signals from the sensors indicating the oscillation of two points on the fluid tube. The phase difference is calculated from the sinusoidal signals. Since the flow calibration factor is proportional to the material and cross sectional properties of the fluid tube, the phase difference measurement and the flow calibration factor are not affected by wear of moving components in the flow meter.
A typical Coriolis mass flowmeter includes one or more transducers (or pickoff sensors), which are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The pickoff sensors are connected to electronic instrumentation. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement, among other things.
Typical Coriolis flow meters measure flow and/or density through the use of a coil and magnet as a pickoff sensor to measure the motion of a meter's vibrating flow tube/tubes. The mass flow rate through the meter is determined from the phase difference between multiple pickoff signals located near the inlet and outlet of the meter's flow tubes. However, it is possible to measure flow using strain gages in place of coil/magnet sensors. A fundamental difference between the two sensor types is that coil/magnet sensors measure the velocity of the flow tubes and strain gages measure the strain of the flow tubes.
Typically manifolds provide the inlet and outlet path for material entry and exit through the flow tubes, and these are generally coupled to flanges that attach to exterior conduits. The manifolds are coupled to the flow tubes and also the case portions. Additionally, spacers are often present between these items. Besides adding expense and weight, the assembly of these parts is cumbersome and prone to error and misalignment.
The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide a manifold for a flowmeter with indexing bosses. An integrated flange is also contemplated. By combining a flange into the manifold, weight and complexity are lowered, and assembly is simplified. The integrated indexing bosses ensure that the manifold is aligned with the flow tubes and other internal flowmeter structures, thus ensuring efficient and accurate assembly. Additionally, the larger surface area provided by the bosses also stiffens the housing and indexes the housing to the manifold.